Optimized running of cold cycles

• Published in: Computers & chemical engineering Vol. 3; no. 1; p. 587
• Main Authors: Lucet, M., Toulet, J.P., Gaultier, J.L., Michel, J.F.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 1979
• ISSN: 0098-1354; 1873-4375
• DOI: 10.1016/0098-1354(79)80101-5

Most of the complex cold cycles that remove heat at different levels of temperature, with one or more parallel compressors, have energy consumptions higher than theoretical. In fact, the control of these cycles is quite difficult: 1. Process cold requirements vary. 2. Discharge pressure fluctuates due to variations in condensing temperature. 3. Thermal load distributions may be very different from the design values of the unit. Consequently, the compressor stages have working conditions very different from design conditions and some stages work at ‘surge limit’. Due to these conditions, operatores select ‘low-risk’ setpoints; compressor recycling is above average and energy consumption is unduly high. The industrial aplicaation developed by Napthachimie involves the use of a computer to control the setpoints of cold cycles; the aim is the reduce the energy consumption of the compressors to a minimum compatible jwith smooth running of the compressors and the process (surge limit, enough heat is removed at sufficiently low temperatures). This application was carried out on the ethylene and propylene cold cycles of our 400,000 T/year steam-cracker. Improvement in our process has been very important. 1. Energy consumption of the compressors dropped by 20%. 2. Running incidents are not so critical due to the automatic correct settings in transien states. Total cost of the operation including hardware and software is about 1 million French Francs; cost savings are 4.5 million French Francs per year.